1. Field of the Invention
This invention relates to a semiconductor light emitting device in which more than three light emitting diodes are equipped to emit various colors of light.
2. Description of the Prior Arts
A prior art multi-color light emitting device is shown in FIG. 5. This device is comprised of a plurality of light emitting diodes (LEDs), each of which emits light having a different wave length.
As shown in FIG. 5a, a multi-color LED lamp includes three light emitting diodes 1a, 1b, and 1c, each of which emits light having a different wave length. These diodes are placed on a lead 2, and molded by plastics 5. Actually, the cathode sides (N sides) of these diodes are electrically connected with the top surface of lead 2. On the other hand, each anode side (P side) of diodes 1a, 1b, or 1c is connected with a respective bonding lead 4a, 4b, or 4c through a corresponding bonding wire 3a, 3b, or 3c.
As shown in FIG. 5b, those light emitting diodes 1a, 1b, and 1c are parallel-connected with each other in the forward direction so as to connect each cathode in common. As a result, each diode can be controlled separately in order to emit a different color light. The lamp, thus, works as a multi-color light emitting device.
In the multi-color LED lamp shown in FIG. 5a, each anode of light emitting diodes 1a, 1b, and 1c should be controlled separately. To this end, the same number of bonding wires as that of diodes placed on lead 2 are required. This fact makes it difficult to reduce the number of parts which compose of the lamp, thus causing a large problem to miniaturize the whole structure of the lamp.
Further, the top surfaces of three bonding leads 4a, 4b, and 4c and the top surface of lead 2 are arranged on a straight line. As a result, the distance between light emitting diode 1b and the corresponding bonding lead 4b in the most outside diameter becomes large, thus making bonding wire 3b longer. This fact also makes bonding works difficult.
In order to solve the above mentioned problem, a structure, in which the anode sides of two light emitting diodes are connected with one bonding lead, can be invented to reduce one bonding lead.
In this structure, however, two light emitting diodes connected with one bonding lead are parallel-connected in the forward direction between lead 2 and the bonding lead. Accordingly, these two diodes cannot be driven separately by external means in order to control their emission independently. Monochromic emission cannot, therefore, be obtained from these two diodes, thus causing restriction on the color tone of the whole LED lamp.
As explained above, in the prior art multi-color LED lamp shown in FIG. 5, it is difficult to obtain a small-sized LED lamp, because each light emitting diode should be driven independently. This fact also deteriorates the efficiency of the assembly works of LED lamps.